Parametric amplifier

ABSTRACT

A parametric amplifier having four substantially identical variable reactance diodes arranged in a bridge circuit supplied with a pump voltage and a signal voltage and developing an idler voltage when these voltage sources are each connected to the diagonally opposed terminals of the bridge and the idler current is contained within the bridge arms. The bridge arrangement provides inherent isolation of two and in some cases the three voltage frequencies. The aforementioned abstract is neither intended to define the invention of the application which, of course, is measured by the claims, nor is it intended to be limiting as to the scope of the invention in any way.

United States Patent [191 Neuf Y 1 Jan. 9, 1973 [75] Inventor:

[73] Assignee: RHG Electronics Laboratory, Inc.,

[54] PARAMETRIC AMPLIFIER Donald Neuf, Wantagh, N.Y.

Farmingdale, L.l., N.Y.

[22] Filed: Feb. 24, 1970 21 Appl. No: 13,437

[52] U.S. Cl. ..330/4.9, 307/883, 330/7 [51] Int. Cl ..H03t 7/00 [58]Field of Search ..330/4.9, 7; 307/883 [56] References Cited UNITEDSTATES PATENTS 2,850,585 1 9/1958 .Green ..330/7 3,433,976 3/1969 Marechal r. ..330/7 3,510,674 5/1970 Biard 3,249,831 5/1966 De Niet.....3,230,464 1/1966 Grace ..330/4.9 3,526,781" 9/1970 Janning ..330/4.9

Primary Examiner-John Kominski Assistant Examiner-Darwin R. HostetterAttorney-Leonard l-l. King [57] ABSTRACT A parametric amplifier havingfour substantially identical variable reactance diodes arranged in abridge circuit supplied with a pump voltage and a signal voltage anddeveloping an idler voltage when these voltage sources are eachconnected to the diagonally opposed terminals of the bridge and theidler current is contained within the bridge arms. The bridgearrangement provides inherent isolation of two and in some cases thethree voltage frequencies.

The aforementioned abstract is neither intended to define the inventionof the application which, of course, is measured by the claims, nor isit intended to be limiting as to the scope of the invention in any way.

6 Claims, 10 Drawing Figures PATENTEDJAN 9l975 3.710.268

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INVENTOR.

DONALD NE ATTORNE PATENIEUJMI 9 ma 3.710.268

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INVENTOR. DONAL-D lly! ATTORNEY PATENTEUJAH 9 I975 SHEET 3 BF 6 $1 GNALCURRENT PUMP CURBEIVT INVENTOR.

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ATTORNEY PATENTEDJAH 9 I973 3.710.268

sum u 0F F] G. 6 INVENTOR. DONALD MEI/F ATTORNEY PATENTED JAN 9 I975SHEET 5 BF 6 FIG. 8

ENVENTOR. DONALD NJ'UF ATTORNEY PATENTEDJAN 9 I973 SHEET 6 [1F 6 FIG. 10

I8 0 P0 WEE DIV/DER INVENTOR. DONALD NEUF ATTORNEY PARAMETRIC AMPLIFIERThis invention relates to amplifiers and specifically to the parametricamplifier employing a variable reactance element.

With the advance in microwave communications, there resulted a greatneed for microwave devices which can amplify one frequency or convert asignal from one frequency to another while providing poweramplification. Mixing devices using non-linear elements have generallybeen used. The mixing devices exchange the energy in a controlled mannerfrom a high power source signal to a lower power signal at a differentfrequency, thereby achieving gain at the latter frequency.

The variable reactance diode has been especially useful in parametricamplifiers because of its low-noise properties. Because of this verysmall amount of internal noise generated during the amplifying process,the parametric amplifier has been used as the front end" of sensitivereceiving stations.

In operation the parametric amplifier generally uses a variablecapacitance diode as the reactance element; The reactance is varied at apump frequency and an input signal to be amplified is applied. The pumpfrequency is generally much higher than the input signal frequency. Theamplifier develops a difference frequency between the pump and signalfrequencies, commonly called the idler frequency. In some modes ofoperations the pump frequency is approximately twice the signalfrequency, whereby the. idler frequency will equal the input frequency.In other modes, the pump frequency is greater than twice the signalfrequency, so that the signal frequency and the idler frequencies differfrom each other.

When the signal and idler frequencies overlap each other, it is referredto as degenerate mode; otherwise it is called non-degenerate mode.

With the idler frequency being different from the signal frequency, theoutput can be taken either at the signal frequency or at the idlerfrequency. When the input and output frequencies are different, theamplifier is commonly referred to as a two-port sum or differencefrequency amplifier, depending upon whether the sum or difference of thepump and signal is used as the output frequency. If the amplifier inputand output terminal is the same, it is termed, one-port operation. Inthe one-port operation a circulator is required to separate the inputand output signals. The input signal is applied to one side of thecirculator and thereafter transferred to a second side of thecirculator. Such circulators are well known in the microwave art.

Owing to the negative input impedance of the oneport-non degeneratemode, andthe subsequent power reflection coefficient which can begreater than unity, it is possible to obtain a reflected signal from theoneport-non degenerate mode, which is greater thanthe input signal. Thisreflected or amplified output is transferred by the circulator to theoutput side. In this manner the inherent one port of the one-port-nondegenerate parametric amplifier is made into a usable system withseparate input and output ports.

In addition to the inherent low noise of the parametric amplifier it isalso preferred to other types of mixers because it can convert thefrequency of an input signal without loss in power; in fact, dependingupon the impedance levels at the signal and! idler frequency terminalsof the parametric amplifier, almost any desirable amount of gain can beachieved with a corresponding reduction in bandwidth.

It is generally desirous to improve the amplifier by making it tunableover a large bandwidth while maintaining low noise and a largegain-bandwidth product. The most significant problem in dealing withimprove ments in parametric amplifiers is providing adequate isolationof the three frequencies (pump, signal and idler). While it is requiredthat the three signals be tightly coupled to the variable reactancediode, it is also necessary that at the same time these signals bedecoupled from each other.

In the prior art, the need forisolation has resulted in designs usingsophisticated coupling mechanisms, and elaborate filters associated witheach signal. In general, these schemes involve a degradation of the gainbandwidth product.

The present invention provides a double-balanced bridge configurationusing at least four variable reactance diodes whereby the signals areeach applied across independent terminals resulting in completeisolation of each frequency from the other. The pump signal is appliedacross one set of cross terminals, the

input signal is applied across a second set of cross terminals, and theidler signal is completely contained within the bridge arms, independentof the circuitry external to the bridge.

Accordingly, it is an object of this invention to provide animprovedparametric amplifier having greater isolation between ports.

Another object is to provide a parametric amplifier using four variablereactance diodes connected in a bridge configuration.

Yet another object is to provide a microwave amplifier using a diodebridge arrangement wherein two of the three frequencies are isolated byvirtue of the balanced properties of the bridge configuration.

Still another object is to provide a variable reactance diode bridgearrangement.

Another object is to provide a one-port parametric amplifier wherein thepump signal and input signal are applied at cross terminals and. theidler signal is completely contained within the bridge.

A further object is to provide a two-port parametric amplifier having adiode bridge arrangement wherein the pump signal and one other signal isapplied at the cross terminals and the idler signal is coupled out ofthe bridge.

Yet another object is to provide a microwave device for use as aparametric amplifier having a variable reactance diode bridgearrangement.

Still yet another object is to provide a bridge arrange ment of fourvariable reactance diode chips mounted in a microwave parametricamplifier.

A still further object is to provide a balanced 3 BRIEF DESCRIPTIOn OFTHE DRAWING FIG. 1 is a block diagram of a generalized one-portamplifier configuration as is known in the art;

FIG. 2 is a block diagram of a generalized two-port amplifierconfiguration as is known in the art;

FIG. 3 is a circuit diagram of the parametric amplifier for a one-portconfiguration in accordance with the teachings of this invention;

FIG. 4 is a circuit diagram of a parametric amplifier for a two-portconfiguration in accordance-with the teachings of this invention;

FIG. 5 is a top view of an assembled microwave parametric amplifierembodiment of this invention for one-port operation;

FIG. 6 is a bottom plan view of the device of FIG. 5;

FIG. 7 is a perspective view of the variable reactance diode bridge asarranged for a microwave parametric amplifier component;

FIG. 8 is a perspective view of the bridge shown in FIG. 7 as it isassembled within an amplifier component;

FIG. 9 is a plan view of an assembled microwave parametric amplifierembodiment of this invention for two-port operation; and

FIG. 10 is a perspective view illustrating another microwave embodimentof one-port parametric amplifier.

Referring to FIG. 1, an input signal is supplied to port (a) of acirculator l0 and is transferred by the circulator to port (b) foramplification by a one-port parametric amplifier 11. The amplifiedoutput signal returns to the circulator through port (b) and is directedto an output port (0) of the circulator. Circulators of this type arewell known in the microwave art and will not be described in detail. Apump source 12 provides the pump frequency for the parametric amplifier11. This figure shows the one-port amplifier configuration as isgenerally used in the art.

The two-port amplifier configuration which is generally used is shown inFIG. 2. For two-port operation the input signal and the output signalare not restricted to be at the same frequency. The input signal issupplied at 15 to a two-port parametric amplifier 13 and the outputsignal is derived at 16. The pump source is provided at 14. In order toinsure stable operation isolators are placed on the input and outputside of the amplifier 17, 18. The isolators are typically designed topass only the frequency of the signal on its side.

FIG. 3 shows a one-port parametric amplifier 11 which can be used in theone-port amplifier configuration shown in FIG. 1. Four substantiallyidentical variable reactance diodes 20, 21, 22, 23 are each connected inrespective arms of a bridge. The diodes are connected such that each oneis reversed from the ones in its adjacent arms. For example, referringto diode as forward, diode 21 would be reversed, diode 22 forward anddiode 23 reversed. Technically, all diodes are reverse biased (at DC)but RF signals are applied in both forward and reversed polarity (seearrows). The signal voltage is supplied at 24 and is applied to thebridge circuit through a signal transformer 25. The input signal isconnected to one set of bridge cross terminals 26, 27. Interconnected inthe supply lines between the transformer 25 and the bridge areinductances 28, 29 which serve as a signal tuning reactance as well asproviding some isolation from any pump signal which may develop on theselines.

The pump voltage is provided at 30 across pump transformer 31 to theremaining set of cross terminals 32, 33. Interconnected between the pumptransformer and the bridge terminals are capacitors 34, 35 which serveas coupling capacitors for the pump voltage as well as providingisolation against the signal voltage and any DC signal.

In prior art amplifiers it has been known to use a pair of identicaldiodes to form a balanced amplifier. The diodes are generally placed inopposition to each other whereby the noise components will be reducedwhile the signal will be enhanced. The circuit of FIG. 3 uses a doublebalanced amplifier design which further provides for signal isolation.For an explanation of the capabilities assume the instantaneous polarityof the signals as shown. Terminal 30a of the pump voltage is positivewith respect to terminal 30b. Similarly terminal 24a of the signalvoltage is positive with respect to terminal 24b. The diodes of thebridge are substantially identical, to provide the same characteristicsand reactances. Accordingly, during balanced operations the voltage dropof the pump voltage through one set of arms including diodes 20 and 21will exactly equal the voltage drop through the other set of armsincluding diodes 23, 22. Since the four diodes are identical, the

pump voltage at terminal 26 will exactly equal the.

pump voltage at terminal 27 and no pump current will flow through lines36 and 37.

The signal voltage applied across terminals 26 and 27 will be the samethrough the set of bridge arms including diodes 21 and 22 and the set ofarms including the diodes 20 and and 23. Also, because of the identicaldiodes, terminals 32 and 33 will have the same signal voltage and nosignal current will flow in lines 38, 39. The pump and signal voltagesare therefore completely isolated from each other. Should there be anyslight unbalance in the diodes, whatever minimal pump current might flowon lines 36, 37 would be blocked by the reactances 29, 28 which aretuned to the signal frequency. Similarly, any signal voltage which mightcause a signal current to flow on lines 38, 39 would be blocked bycapacitors 34, 35.

With the voltages of the pump and signal sources as shown in FIG. 3, thesignal current would flow from terminal 26 to terminal 27 through bothparallel paths including diodes 23, 20 and 22, 21. The pump currentwould flow from terminal 32 to terminal 33 through the two parallelpaths, the one containing diode 21, 20; the other containing the diodes22, 23.

As a result of the diode arrangement and the polarity of the appliedpump and signal voltages, the difference voltage or idler frequencysignal is excited within the bridge arms such that idler current will becompletely contained within the bridge arms. Furthermore, it will beindependent of external circuit loading since at the pump and signalterminals no idler voltage exists.

In the double balanced bridge circuit the three signals will thereforebe isolated from each other. The pump and signal voltages will beisolated because of the inherent balance of the two sides of the bridge.The idler current will be isolated because of the resultantcancellations of the idler at the signal and pump terminals.

The reactance characteristic of the variable reactance diode is such asto vary as a function of the reverse voltage across the diode. As thereverse bias voltage is increased the capacitance decreases. Thusconsiderable adjustment in the capacitance can be obtained by varyingthe bias on the diodes. RF chokes 48 and 41 are added at terminals 32and 33 for introducing the DC bias on the diodes. RF chokes 42 and 43are added at terminal 26 and 27 for the DC bias return.

FIG. 4 shows a two-port parametric amplifier 13 which can be used in thetwo-port amplifier configuration of FIG. 2. The basic concept of thetwo-port amplifier is similar to that discussed for the one-portamplifier in connection with FIG. 3. The additional requirements arethat the output be taken at either the signal voltage or more usuallythe idler voltage. In FIG. 4

. components which are the same as those of FIG. 3 are similarlynumbered.

The bridge consists of four arms each containing variable reactancediodes 20, 21, 22, 23. The diodes are placed so that each is in the samedirection as one adjacent arm and in opposite direction to theotheradjacent arm. Following the designation of FIG. 3 wherein diode wasthere in the forward direction, in FIG. 4 diode 20 is in the reversedirection, diode 21 in the forward direction, diode 22 in the forwarddirection and diode 23 in the reverse direction.

Pump voltage is applied at 30 across the transformer 31 to terminals 32and 33 by means of lines 38 and 39. Capacitors 34 in line 38 and 35 inline 39 serve as pump coupling capacitors and also provide a DC blockand isolate the signal voltage. The signal voltage is applied at 24across transformer by means of lines 36 and 37 to the same terminals32,33 as the pump voltage. Inductors 28 in line 36 and 29 in line 37provide a signal tuning reactance and serves to isolate the pump voltagefrom the signal voltage. In addition, capacitor 44 in series withinductor 28 and capacitor 45 in series with inductor 29 acts as DCblocking capacitors permitting only signal voltage to pass.

The idler voltage output is taken at 46 from bridge terminals 26, 27through lines 50, 51 and across transformer 47. Capacitors 48 in line 50and 49 in line 51 serve as DC blocking capacitors and permit idlervoltage passing through. The DC bias for the diodes is provided throughRf chokes 52, 53, each connected to one i of the idler lines 50, 51 andRF choke 52 is connected to the positive supply, and RF choke 53 isconnected to the DC negative supply.

To understand the operation of the circuit of FIG. 4, the variousinstantaneous voltages have polarities as shown. Pump voltage supplyterminal a is positive with respect to 30b. The voltage from terminals32 to 33 is across parallel paths comprising diodes 20, 21 and 23, 22.Because diodes 20 and 23 are oppositely biased, their reactances differand a small pump voltage will appear between terminals 26 and 27.

The signal voltage at 24 has a polarity such that 24 is a positive withrespect to 24b. The signal voltage will appear between terminals 32 and33. The pump voltage and the signal voltage will combine in each diodeto form the difference or idler voltage at terminals 26, 27. The idlervoltage will be the output voltage appearing at 46 with terminals 464positive and 46b negative.

With the voltage polarities as shown, the currents in the bridge will beas indicated. The pump and signal currents flow concurrently through thebridge from terminals 33 to terminal 32, through both parallel bridgepaths, including diodes 20, 23 and 21, 22. The idler between the idlersignal and the other signals. Because of the substantially identicaldiodes and their orientation there will be no idlervoltage betweenterminals 32 and 33. The pump and signal voltages will thus be isolatedfrom the idler voltage. In this configuration, the bridge does notprovide any inherent isolation between the pump and signal voltages.However, the pump and signal frequencies are sufficiently separated suchthat the simple filtering networks of capacitors 34, 35 and inductors28, 29 are sufficient to isolate the signal and pump voltages. Thereactance of the pump coupling capacitors 34, 35 will be considerablyhigher at the low signal frequency thus providing the necessary pump tosignal isolation. The inductive reactance of inductors 28, 29 wouldprevent the pump from coupling to the signal port.

If the particular use was such that the signal and pump frequencies wereclose together and the idler frequency was the lowest and separated fromtheothers, FIG. 4 would be altered. such that the idler frequency wouldbe taken out at terminals 32, 33 and the signal voltage would be appliedat the opposite terminals 26, 27. In this case, by interchanging, theidler and signal supply circuits, the inherent bridge configurationwould isolate the signal from the pump while the idler voltage being ata separated frequency, would be isolated by filter means.

Although the circuit of FIG. 4 is best used for a twoport amplifierconfiguration, it can also be used for a one-port configuration whereaccess to the idler circuit is required. The circuit of FIG. 4 allowsexternal coupling to the idler circuit in order'to vary the resistanceof the idler circuit. The output from the circuit of FIG. 4 when used asa one-port amplifier would be taken from the signal voltage terminals24a and 24b.

FIGS. 5 and 6 indicated one microwave embodiment of the one-portparametric amplifier shown in FIG. 3. FIG. 5 represents the top view ofthe device and FIG. 6 shows the ground side of the device. A housing 55consists of a frame holding a dielectric substrate sheet 56 securelyfastened to the frame on two sides 57, 58. A space is left 59, 60between the substrate 56 and the remaining sides of the frame. The spaceis filled in with lossy RF material to reduce reflections. Situated ateither end of the frame members 57,58 are coaxial cable connections 61,62 securely fastened to the housing 55. Situated on the substrate arefour variablereactance diodes electrically connected in a bridgearrangement as hereinbefore described in connection with FIG. 3. Thediodes are attached with two diodes, 20, 23 connectedon the top side ofthe substrate and two diodes 22, ZIconnected on the ground side of thesubstrate.

FIG. 7 shows a schematic of the packaging arrangement of the diodebridge assembly. The four diodes 20, 21, 22, 23, electrically connectedas hereinbefore described are physically placed such that diodes 20 and23 are in a single plane with an electrical contact 32 connectedtherebetween. Similarly diodes 21 and 22 are in the same plane. Diodes20 and 21 are electrically interconnected in common with terminal 26 anddiodes 22 and 23 have terminal 27 electrically interconnectedtherebetween.

Referring back to FIGS. and 6, coaxial connection 61 is used to providethe signal voltage while connection 62 is for the pump voltage. Inbetween the coaxial connections and the diode package is placed amicrostrip transformer. The signal transformer is comprised of themetallic strips 63a and 63b having the dielectric substratetherebetween. The pump transformer comprises metallic strips 64a and 64bwith the dielectric substrate between them.

The coaxial input to the amplifier is unbalanced while the microstriplines needed to power the diodes is balanced. A balancing unit or balunis used to accomplish the transition from the unbalanced to the balancedcondition. This is accomplished by gradually tapering the conventionalground plane side of the metallic strip material until it becomes equalin width to the metallic strip on the opposite side of the dielectric.The signal balun is comprised of sections 65a on the top side and 65b onthe conventional ground side of the dielectric. Metallic strip 65b istapered from its broad width at the signal input terminal 61, until itsnarrow width at the transformer connection. The narrow width of strip65b is made equal to the width of the balun strip 65a. Similarly for thepump balun, the conventional ground side metallic strip 66b is taperedfrom its broad width at the pump input terminal 62 to a narrow widthequal to the top side strip 66a. The narrow end is connected to thetransfer 64.

FIG. 8 illustrates a detail view of the diode package of FIGS. 5, 6 andshows the interconnections between the diode bridge and the signal andpump voltages. The interconnecting lead 26 between diodes and 21 (FIG.7) is brought to the top side of the substrate and is connected to oneend of the signal transformer 63a by means of signal tuning inductance28. On the conventional ground side, the other end of the signaltransformer 63b would be connected to terminal 27 by means of signaltuning inductance 29. One end of the pump transformer 64a is connectedto tenninal 32 by means of the pump coupling capacitance 34. The otherend of the pump transformer 64b would be connected on the ground side toterminal 33 by means of coupling capacitor 35.

In order to introduce DC bias miniature coils wound on finely threadeddielectric screws 67 are used. The DC bias is introduced through an RFbypass capacitor included in terminals 68a and 68b, then through coils67a and 67b to the terminals 32, 33. The DC bias return is taken outthrough RF coil 670.

FIG. 9 illustrates a possible microwave equivalent of the two-portparametric amplifier shown in FIG. 4. The basic configuration of thediode package, the balanced microstrip transformers and baluns aresimilar to that described for FIGS. 5 through 8. For the two-portconfiguration, however, the diode would be biased as shown in F IG. 4.Also, for the two-port case a separate port must be provided for theidler voltage. In FIG. 9 coaxial connector 61 provides the pump inputwhich is connected by means of the microstrip balun and transformer toterminal 32. The idler output is taken from terminal 26 through themicrostrip to coaxial connector 62. The signal voltage is coupled to thediode bridge by means of coaxial connector 69. Instead of microstrip, acoupling coil of fine wire wound on to a dielectric member 70 is used.The coupling coil serves to isolate the pump signal as well as provide'a tuned reactance for the signal voltage. The signal and idlerterminals can be interchanged depending upon the relative frequencies ashereinbefore described.

FIG. 10 illustrates another possible microwave equivalent of a one-portparametric amplifier as described in FIG. 3. The bridge of variablereactance diodes 20, 21, 22, 23 have cross terminals 32, 33 and 26, 27as before. The pump voltage is provided by a waveguide type feed throughpump waveguide 71 to the terminals 32, 33 representing one port. Thesignal input is provided through a phase reversing power divider 72. Thesignal input is coaxial providing a hybrid feed as is known in the art.The coaxial signal input is connected to opposite bridge terminals 26,27. The idler currents are generated such that they are confined to thebridge diodes and are independent of the waveguide circuitry ashereinbefore explained.

It is understood that the diode bridge is usually mounted in a ceramicor glass package to facilitate connections to other components. However,the diode could also be mounted as chips without the aid of specialpackaging.

While the present invention has been described with reference toparticular embodiments thereof, it will be understood that numerousmodifications may be made by those skilled in the art without actuallydeparting from the scope of the invention.

What I claim as new and desire to secure by said Let ters Patent is:

l. A parametric amplifier comprising:

a. four substantially matched variable reactance diodes connected in adouble balanced bridge arrangement, each of said diodes positioned inits respective bridge arm in opposite poled arrangement with the diodesin both adjacent bridge arms;

b. means for supplying a pump voltage frequency across a first pair ofdiagonally opposing bridge terminals;

c. means for supplying a signal voltage across a second pair ofdiagonally opposing bridge terminals; and

(1. means for containing the developed idler voltage completely withinthe bridge arrangement and independent of external loads.

2. A parametric amplifier as in claim 1 and wherein said means forsupplying a pump voltage frequency and said means for connecting asignal voltage frequency each include filter means to permit the passageof the frequency supplied but isolating the other frequencies.

3. A parametric amplifier as in claim 1 and further including DC biasmeans for applying and returning a DC bias to said diodes.

4. A parametric amplifier as in claim 1 for use at microwave frequenciesas a' one-port amplifier further comprising a housing, a dielectricsubstrate mounted in said housing, first and second coaxial connectionsfor respectively connecting with the pump frequency source and thesignal frequency source, said coaxial connections mounted on saidhousing, said diode bridge arrangement mounted onto said substrate,first the opposite side of the substrate whose width at one end matchesthe coaxial connections and being tapered until the other end matchesthe width of said first metallic strip, and a plurality of miniaturecoils connected to said bridge for supplying and removing a DC bias fromeach side.

5. In a parametric amplifier having a double balanced bridge arrangementof four substantially matched variable. reactance diodes and suppliedwith pump and signal frequencies along unbalanced coaxial cables, thebalancing arrangement comprising balanced microstrip baluns having afirst and second metallic strip separated by a dielectric wherein saidfirst metallic strip is at a uniform width and said second metallicstrip is tapered from its broad end matching the unbalanced coaxialcable to its narrow end matching the width of said first metallic strip.

6. A parametric amplifier as in claim 5 wherein each of said diodes isarranged within its respective bridge arm in opposite poled arrangementwith the diodes in both adjacent bridge arms.

1. A parametric amplifier comprising: a. four substantially matchedvariable reactance diodes connected in a double balanced bridgearrangement, each of said diodes positioned in its respective bridge armin opposite poled arrangement with the diodes in both adjacent bridgearms; b. means for supplying a pump voltage frequency across a firstpair of diagonally opposing bridge terminals; c. means for supplying asignal voltage across a second pair of diagonally opposing bridgeterminals; and d. means for containing the developed idler voltagecompletely within the bridge arrangement and independent of externalloads.
 2. A parametric amplifier as in claim 1 and wherein said meansfor supplying a pump voltage frequency and said means for connecting asignal voltage frequency each include filter means to permit the passageof the frequency supplied but isolating the other frequencies.
 3. Aparametric amplifier as in claim 1 and further including DC bias meansfor applying and returning a DC bias to said diodes.
 4. A parametricamplifier as in claim 1 for use at microwave frequencies as a one-portamplifier further comprising a housing, a dielectric substrate mountedin said housing, first and second coaxial connections for respectivelyconnecting with the pump freQuency source and the signal frequencysource, said coaxial connections mounted on said housing, said diodebridge arrangement mounted onto said substrate, first and secondbalanced microstrip transformers each respectively connected to saidfirst and second pair of diagonally opposing bridge terminals, first andsecond balanced microstrip baluns respectively interconnected betweensaid coaxial connections and said transformers, said baluns having afirst metallic strip on one side of said substrate with a uniform widthwhose width matches the transformer, and a second metallic strip on theopposite side of the substrate whose width at one end matches thecoaxial connections and being tapered until the other end matches thewidth of said first metallic strip, and a plurality of miniature coilsconnected to said bridge for supplying and removing a DC bias from eachside.
 5. In a parametric amplifier having a double balanced bridgearrangement of four substantially matched variable reactance diodes andsupplied with pump and signal frequencies along unbalanced coaxialcables, the balancing arrangement comprising balanced microstrip balunshaving a first and second metallic strip separated by a dielectricwherein said first metallic strip is at a uniform width and said secondmetallic strip is tapered from its broad end matching the unbalancedcoaxial cable to its narrow end matching the width of said firstmetallic strip.
 6. A parametric amplifier as in claim 5 wherein each ofsaid diodes is arranged within its respective bridge arm in oppositepoled arrangement with the diodes in both adjacent bridge arms.